12 
AMERICA THE OLD WORLD. 
a whole than their successors, who far excel 
them in their knowledge of special points, but 
often lose their grasp of broader relations in the 
more minute investigation of details. TV hen geo- 
logists first turned their attention to the physical 
history of the earth, they saw at once certain 
great features which they took to be the skeleton 
and basis of the whole structure. They saw the 
great masses of granite forming the mountains 
and mountain-chains, with the stratified rocks 
resting against their slopes ; and they assumed 
that granite was the first primary agent, and that 
all stratified rocks must be of a later formation. 
Although this involved a partial error, as wo 
shall see hereafter, when we trace the upheavals 
of granite even into comparatively modern peri- 
ods, yet it held an important geological truth 
also ; for, though granite formations are by no 
means limited to those early periods, they are 
nevertheless very characteristic of them, and are 
indeed the foundation-stones on which the phys 
ical history of the globe is built. 
Starting from this landmark, the earlier geol- 
ogists divided the world’s history into three peri- 
ods. As the historian recognizes as distinct 
phases in the growth of the human race Ancient 
History, the Middle Ages, and Modern History, 
so they distinguish between what they call the 
Primary period, when, as they believed, no life 
